Joseph Pankert

Physical properties of the HCT EUV source

The paper describes the physical properties and recent technical advances of the hollow cathode triggered pinch device (HCT) for the generation of EUV radiation. In previous publications we have demonstrated continuous operation of the untriggered device at 1 kHz in pure Xe. The newer generations operate with a triggering facility which allows a wider parameter space under which stable operation is possible. Repetition frequencies of up to 4 kHz could be demonstrated. Many of the experiments are performed in repetitive bursts of variable lengths and spacing. This allows also to demonstrate that there is only little transient behavior upon switching on and off the source. Conversion efficiencies into the 2 percent frequency band around 13.5 nm are about 0.4 percent in 2p, comparable to the values reported from other groups. Another important parameter is the size of the light emitting region. Here we have studied the influence of electrode geometry and flow properties on the size, to find a best match to the requirements of the collection optics. A major problem for the design of a complete wafer illumination system is the out-of-band portion of the radiation. Especially the DUV fraction of the source spectrum is a concern because it is also reflected to some extend by the Mo-Si multilayer mirrors. We show that the source has a low overall non-EUV part of the emission. In particular, it is demonstrated that there is very little DUV coming out of the usable source volume, well below the specified level.

Frequency scaling in a hollow-cathode-triggered pinch plasma as radiation source in the extreme ultraviolet

The hollow-cathode triggered discharge extreme ultraviolet source is based on the same principle as pseudospark switches. The electrode geometry consists of a planar anode and cathode with central opposing holes, the one on the cathode side being connected to the hollow cathode. Radiation is generated by magnetic compression of the working gas under high-current operation. Essential for the operation is that the pressure and voltage are chosen to be on the left side of the Paschen curve to insure insulation of the gap between the electrodes. However, this insulation of the electrode system needs to be reinstalled after breakdown. Typical recovery times of a xenon-based system are down to 100 /spl mu/s, depending on the electrode geometry. It will be shown that the decay of the electron density in the hollow cathode is the limiting process. Investigation of the recovery mechanism has led to a design that allows operation above 4 kHz which is close to the required frequency for extreme ultraviolet lithography.

Ultrasonic attenuation by the vortex lattice of Bi1.6Pb0.4Sr2Ca2Cu3Oy

Abstract The ultrasonic attenuation and velocity shift, induced by the vortex lattice of high- T c superconductors, are measured as a function of field, frequency and temperature. Two different ceramic samples, both of the Bi-2223 composition, are investigated: One is an isotropic and the other one a strongly textured sample. For the latter, eight different modes are analysed, differing from each other by the relative orientation of the wave vector, the displacement vector of sound and the applied magnetic field. The field induced attenuation shows a distinct peak and the sound velocity a step at the same temperature. These effects are explained by a transition of the flux line lattice from a pinned into a depinned state. The results can be described quantitively by a simple model based on flux line diffusion.

EUV sources for the alpha-tools

In this paper, we report on the recent progress of the Philips Extreme UV source. The Philips source concept is based on a discharge plasma ignited in a Sn vapor plume that is ablated by a laser pulse. Using rotating electrodes covered with a regenerating tin surface, the problems of electrode erosion and power scaling are fundamentally solved. Most of the work of the past year has been dedicated to develop a lamp system which is operating very reliably and stable under full scanner remote control. Topics addressed were the development of the scanner interface, a dose control system, thermo-mechanical design, positional stability of the source, tin handling, and many more. The resulting EUV source-the Philips NovaTin(R) source-can operate at more than 10kW electrical input power and delivers 200W in-band EUV into 2π continuously. The source is very small, so nearly 100% of the EUV radiation can be collected within etendue limits. The lamp system is fully automated and can operate unattended under full scanner remote control. 500 Million shots of continuous operation without interruption have been realized, electrode lifetime is at least 2 Billion shots. Three sources are currently being prepared, two of them will be integrated into the first EUV Alpha Demonstration tools of ASML. The debris problem was reduced to a level which is well acceptable for scanner operation. First, a considerable reduction of the Sn emission of the source has been realized. The debris mitigation system is based on a two-step concept using a foil trap based stage and a chemical cleaning stage. Both steps were improved considerably. A collector lifetime of 1 Billion shots is achieved, after this operating time a cleaning would be applied. The cleaning step has been verified to work with tolerable Sn residues. From the experimental results, a total collector lifetime of more than 10 Billion shots can be expected.

Influence of grain boundaries on complex permeability in MnZn ferrites

Abstract The permeability of ceramic soft magnetic ferrites distinctly depends on grain size. A model will be presented which accounts for this dependency in a quantitative fashion and without any adjustable parameter. This model involves boundary conditions for the spin system at the exchange-decoupled interfaces of adjacent grains and an inhomogeneous free energy density which brings the domain wall width as a natural length scale into the problem. It will be shown that this scale will precisely determine the grain size beyond which the permeability significantly starts to decrease.

Ultrasonic attenuation in high-Tc superconductors: a new approach to the problem of flux pinning

Measurements of the transverse sound attenuation and velocity in ceramic YBa2Cu3Ox superconductors were performed with and without a magnetic field. We observe a pronounced peak in the field-induced attenuation and an increase of the velocity at low temperatures. We attribute these effects to the transition of a rigidly pinned flux line lattice into a depinned state at higher temperatures and give a quantitative explanation in terms of thermally assisted flux flow. Depinning temperatures show a drastic dependence on the oxygen stoichiometry.

Magnetoacoustic determination of pinning energies in high-Tc superconductors

Abstract By means of the recently established ultrasonic technique, activation energies for the vortex lattice of various high- T c superconductors are determined. These are deduced from the characteristic maximum in the field induced attenuation which is associated with the depinning of the flux line lattice from the superconductor. It is demonstrated that the resulting energies are basically the same as those determined by resistive measurements on single crystals, even though the ultrasound experiments are performed on ceramic bulk samples.

Status report on EUV source development and EUV source applications in EUVL

Extreme ultraviolet lithography (EUVL) is the leading technology for patterning at the 32 nm technology node and be-yond. EUVL light at 13.5 nm is used to print circuits. This light is produced by heating fuel (Xe, Sn) in EUV sources to a very high temperature by using either magnetic compression or laser irradiation. Today EUV source power remains the number one concern for implementation of EUVL in high volume manufacturing. Over the last few years, much pro-gress has been made in EUV source performance and availability. Today, alpha level high power (~10 W) EUV sources have been integrated in alpha level EUVL scanners. Medium and low power EUV sources are used for in-house metrol-ogy and performance studies on EUV mask blanks, EUV masks, photoresists, and optical elements. These compact dis-charge sources with medium power in the range of 10-100 mW/sr/2% bandwidth and low power EUV tubes are being used by various R&D labs for development of mask, optics, and resists. Previously, development of EUVL was mostly located at beamlines; today, these low power EUV sources are instrumental in allowing in-house R&D projects. In this paper, the latest status of high power EUV sources, low and medium power metrology sources, and some of their appli-cations are described.

Sound attenuation in the mixed state of high-Tc superconductors

The attenuation and dispersion of ultrasound in high-T c superconductors exposed to a magnetic field is studied. The pinning interaction of the flux line lattice (FLL) with the crystal leads to an enhanced sound velocity and a peak in the attenuation at the depinning temperature. On the grounds of thermally assisted flux flow (TAFF), both the attenuation and the dispersion are predicted without an adjustable parameter.

Status of Philips' extreme UV source

The paper describes progress of the Philips’ hollow cathode triggered (HCT) gas discharge EUV source. The program has been focussed on three major areas: (1) Studying the basic physics of ignition, pinch formation and EUV generation. The paper reports on progress in this area and particularly describes the underlying atomic physics both for Xe and Sn. (2) Discharge based on Sn. Results on overall efficiency more than 5 times the Xe efficiency are reported as well as high frequency operation up to 6.5 kHz. This system shows all the necessary ingredients for scaling to production power levels. (3) Integration of the Xe source in an alpha tool. Results on integration issues like electrode life time, collector life time and dose control will be presented.